Dual material planting equipment for efficiently delivering both fertilizer and seed into furrows in the ground are well known. Examples of such planting equipment are disclosed in U.S. Pat. Nos. 5,331,907 and 5,396,851 both to Norbert Beaujot. These patents describe the general planting process of opening a first furrow in the ground into which fertilizer is deposited and opening a second furrow laterally and vertically spaced from the first into which seed is deposited. Generally, the placement of fertilizer and seed is accomplished by separate material dispensing implements such as knives or discs that are towed across a field by a tractor or suitable vehicle equipped with a supply of fertilizer and seed.
Agronomic research indicates that the two furrows should preferably have a lateral separation of approximately 38 mm (1.5 inches) and a vertical spacing of approximately 19 mm (0.75 inches) for optimal germination and growing conditions. Therefore, the material dispensing implements of the planting equipment need to be vertically and horizontally spaced, correspondingly.
Once the fertilizer and seed have been deposited, a packer wheel compresses the soil that has flowed back into the furrows to bury the fertilizer and seed bringing the soil into contact with the seed, which is essential for germination, and sealing the soil surface over the furrows. The depth of the seed and fertilizer placement is measured from the compacted surface left by the packer wheel.
The depth of the seed and fertilizer placement below the soil surface is adjustable to accommodate different fertilizer and seed combinations, different seed types, and different soil type and moisture. In prior art equipment for performing the planting process described above, the optimal relative vertical spacing of the fertilizer and seed dispensing implements tends to be altered when vertical adjustments are made. For example, vertical adjustment of the forward fertilizer dispensing implement generally involves independent vertical movement of the implement, while vertical adjustment of the rearward seed dispensing implement relies on pivoting of the arm supporting the rearmost packer wheel. At the same time, in prior art designs, pivoting of the packer wheel arm also affects the vertical position of the forward fertilizer dispensing implement but not to the same extent as the rearmost seed dispensing implement. In other words, with prior art planting equipment, it is usually necessary to independently adjust the position of both fertilizer and seed dispensing implements when adjusting the vertical depth of planting to maintain the same vertical distance between the implements, and hence, the same optimal vertical separation between the fertilizer and seed furrows.